1. Field of the Invention
The present invention relates to an image pickup apparatus enabling to photograph an object under an appropriate exposure by making a light emitting device such as a light emitting diode (LED) emit light, and the control method of the image pickup apparatus.
2. Description of Related Art
Conventionally, a strobe using a xenon tube has been generally used with an objective of supplementing an insufficient light amount at the time of photographing and providing an illumination effect to a photographing image, in an image processing apparatus such as an electronic camera arranged to record and reproduce still images and moving images using a memory card including a solid-state memory device, as a recording medium.
A strobe is characterized to have a construction of applying high voltage electric power charged in a main capacitor having a large capacity to a xenon tube in response to a trigger signal to make the xenon tube emit light. Consequently, an image pickup apparatus needs a boosting circuit, a trigger device, a main capacitor and the like besides a light emitting unit (the xenon tube), which have been a fetter of the reduction in cost and miniaturization. Moreover, in case of performing. continuous shooting with light being emitted, a time for charging the main capacitor after the light emission is required, and there has been a problem of lengthening a photographing interval.
Consequently, it is a high luminance type light emitting diode (LED) that has been watched in recent years. Because the LED does not need a high voltage and a main capacitor having a large capacity, the number of parts becomes small, and the equipment can be miniaturized at a low cost. Moreover, because no charging time to a capacitor is necessary, the LED scarcely influences the photographing intervals at the time of light emitting. A plurality of image pickup apparatuses using such an LED as a subsidiary light source has been proposed (see, for example, Japanese Patent Application Laid-Open No. 2003-114463 and Japanese Patent Application Laid-Open No. 2002-207236).
However, many image pickup apparatuses each using an LED as a substitute of a strobe severally operate with a battery. Because the LED does not emit light by already charged electric power like a xenon tube when the LED is made to emit light at a high luminance, the current amount of an image pickup apparatus increases during light emitting, and the electric power source voltage drops. At this time, there is a case where the electric power source of the image pickup apparatus falls in a low battery (LB) state, i.e. a sate in which a battery has not a voltage necessary for a normal photographing drive of the image pickup apparatus, during an exposure period or memory access. Consequently, there is a case where photographing cannot be normally completed.